Froth flotation deinking process for paper recycling

Abstract

The present invention provides a froth flotation process for the separation of paper and wood fibers from printed and copying inks and other contaminants during the recycling of paper. A liquid solution containing a frothing agent is applied from the top of a froth flotation device, preferably in the form of a spray, to the upper surface or portion of an aqueous pulp slurry present in the device, or of a froth phase produced in the device, prior to or during the froth flotation process.

What is claimed is: 
     
       1. A method for the froth flotation separation of fibers of wastepaper or wood fibers from ink or other contaminants, said method comprising: (a) introducing an aqueous slurry of wastepaper containing one or more contaminants into a froth flotation device having an upper portion and a lower portion, said slurry having an upper surface and a lower surface, wherein no frothing agent is added to said slurry prior to introducing said slurry into said froth flotation device;   (b) introducing a pressurized nonreactive gas into said lower portion of said device for upward flow through said device;   (c) introducing a solution containing a frothing agent to said upper surface of said slurry, or to an upper portion of said slurry, whereby a froth layer becomes formed in said upper portion of said device and a fraction which does not contain froth remains in said lower portion of said device, or introducing a solution containing a frothing agent to an upper surface or portion of a froth layer formed in said device, said frothing agent being introduced in an amount which is effective for forming a froth; and   (d) withdrawing said fraction which does not contain froth from said device, said fraction containing said fibers; wherein said solution is introduced to said slurry or froth layer prior to, during or after the introduction of said gas into said device, and wherein said process is performed for a period of time which is sufficient to separate at least some of said contaminants from said fibers.     
     
     
       2. The method of claim 1, wherein said solution is introduced to said slurry or froth layer prior to the introduction of said gas into said device. 
     
     
       3. The method of claim 1, wherein said solution is introduced to said slurry or froth layer during the introduction of said gas into said device. 
     
     
       4. The method of claim 2, wherein said solution is applied to about the upper 50 cm of said slurry or froth layer. 
     
     
       5. The method of claim 3, wherein said solution is applied to about the upper 50 cm of said slurry or froth layer. 
     
     
       6. The method of claim 4, wherein said solution is applied to about the upper 4 cm of said slurry or froth layer. 
     
     
       7. The method of claim 5, wherein said solution is applied to about the upper 4 cm of said slurry or froth layer. 
     
     
       8. The method of claim 6, wherein said solution is applied to about the upper 2 cm of said slurry or froth layer. 
     
     
       9. The method of claim 7, wherein said solution is applied to about the upper 2 cm of said slurry or froth layer. 
     
     
       10. The method of claim 8, wherein said solution is applied to the upper surface of said slurry or froth layer. 
     
     
       11. The method of claim 9, wherein said solution is applied to the upper surface of said slurry or froth layer. 
     
     
       12. The method of claim 1, wherein said solution is introduced as a spray above the upper surface of said slurry. 
     
     
       13. The method of claim 6, wherein said solution is introduced as a spray above the upper surface of said slurry. 
     
     
       14. The method of claim 7, wherein said solution is introduced as a spray above the upper surface of said slurry. 
     
     
       15. The method of claim 12, wherein said spray is formed by a pressure atomizer positioned no higher than about 50 cm above said upper surface of said slurry. 
     
     
       16. The method of claim 13, wherein said spray is formed by a pressure atomizer positioned no higher than about 50 cm above said upper surface of said slurry. 
     
     
       17. The method of claim 14, wherein said spray is formed by a pressure atomizer positioned no higher than about 50 cm above said upper surface of said slurry. 
     
     
       18. The method of claim 15, wherein said pressure atomizer is positioned no higher than about 4 cm above said upper surface of said slurry. 
     
     
       19. The method of claim 16, wherein said pressure atomizer is positioned no higher than about 4 cm above said upper surface of said slurry. 
     
     
       20. The method of claim 17, wherein said pressure atomizer is positioned no higher than about 4 cm above said upper surface of said slurry. 
     
     
       21. The method of claim 12, wherein said solution contains from about 0.001 to about 500,000 mg of frothing agent per liter of water, wherein said solution is introduced at a spray flow rate ranging from about 0.001 gallons per second to about 100 kilogallons per second for a period of time ranging from about 10 seconds to about 60 minutes, wherein the amount of frothing agent delivered ranges from about 0.001 to about 500 g per kg of dry pulp recovered from said method, and wherein said method is performed for a period of time ranging from about 10 seconds to about 60 minutes. 
     
     
       22. The method of claim 13, wherein said solution contains from about 0.001 to about 500,000 mg of frothing agent per liter of water, wherein said solution is introduced at a spray flow rate ranging from about 0.001 gallons per second to about 100 kilogallons per second for a period of time ranging from about 10 seconds to about 60 minutes, wherein the amount of frothing agent delivered ranges from about 0.001 to about 500 g per kg of dry pulp recovered from said method, and wherein said method is performed for a period of time ranging from about 10 seconds to about 60 minutes. 
     
     
       23. The method of claim 14, wherein said solution contains from about 0.001 to about 500,000 mg of frothing agent per liter of water, wherein said solution is introduced at a spray flow rate ranging from about 0.001 gallons per second to about 100 kilogallons per second for a period of time ranging from about 10 seconds to about 60 minutes, wherein the amount of frothing agent delivered ranges from about 0.001 to about 500 g per kg of dry pulp recovered from said method, and wherein said method is performed for a period of time ranging from about 10 seconds to about 60 minutes. 
     
     
       24. The method of claim 21, wherein said solution contains from about 10 to about 100 mg of frothing agent per liter of water, wherein said solution is introduced at a spray flow rate ranging from about 1 to about 100 gallons per second for a period of time ranging from about 1 to about 10 minutes, wherein the amount of frothing agent delivered ranges from about 0.1 to about 5 g per kg of dry pulp recovered from said method, and wherein said method is performed for a period of time ranging from about 5 to about 10 minutes. 
     
     
       25. The method of claim 22, wherein said solution contains from about 10 to about 100 mg of frothing agent per liter of water, wherein said solution is introduced at a spray flow rate ranging from about 1 to about 100 gallons per second for a period of time ranging from about 1 to about 10 minutes, wherein the amount of frothing agent delivered ranges from about 0.1 to about 5 g per kg of dry pulp recovered from said method, and wherein said method is performed for a period of time ranging from about 5 to about 10 minutes. 
     
     
       26. The method of claim 23, wherein said solution contains from about 10 to about 100 mg of frothing agent per liter of water, wherein said solution is introduced at a spray flow rate ranging from about 1 to about 100 gallons per second for a period of time ranging from about 1 to about 10 minutes, wherein the amount of frothing agent delivered ranges from about 0.1 to about 5 g per kg of dry pulp recovered from said method, and wherein said method is performed for a period of time ranging from about 5 to about 10 minutes. 
     
     
       27. The method of claim 24, wherein said solution contains from about 16 to about 40 mg of frothing agent per liter of water, wherein said solution is introduced at a spray flow rate of about 1.4 gallons per second for a period of time ranging from about 107 to about 600 seconds, wherein the amount of frothing agent delivered ranges from about 0.1 to about 0.5 g per kg of dry pulp recovered from said method, and wherein said method is performed for about 10 minutes. 
     
     
       28. The method of claim 25, wherein said solution contains from about 16 to about 40 mg of frothing agent per liter of water, wherein said solution is introduced at a spray flow rate of about 1.4 gallons per second for a period of time ranging from about 107 to about 600 seconds, wherein the amount of frothing agent delivered ranges from about 0.1 to about 0.5 g per kg of dry pulp recovered from said method, and wherein said method is performed for about 10 minutes. 
     
     
       29. The method of claim 26, wherein said solution contains from about 16 to about 40 mg of frothing agent per liter of water, wherein said solution is introduced at a spray flow rate of about 1.4 gallons per second for a period of time ranging from about 107 to about 600 seconds, wherein the amount of frothing agent delivered ranges from about 0.1 to about 0.5 g per kg of dry pulp recovered from said method, and wherein said method is performed for about 10 minutes.